1. Field of the Invention
The present invention relates to a bearing and a shaft, and particularly to a method of manufacturing a bearing or a shaft with hydrodynamic pressure generating grooves.
2. Description of Related Art
At present, hydrodynamic bearings are widely used in spindle motors in devices, such as compact disc (CD) drivers, digital video disc (DVD) drivers, hard disk drivers, laser beam printers, floppy disk drivers or in heat-dissipation fans. Spindle motors require a hydrodynamic bearing of small size, high rotational accuracy and long life.
A typical hydrodynamic bearing defines a bearing hole therein. A shaft is rotatably received in the bearing hole. A plurality of herringbone-shaped grooves are defined either in an inner circumferential surface of the bearing or in an external circumferential surface of the shaft. The grooves can accommodate lubricant, such as oil. During rotation of the shaft, the lubricant is driven by the rotating shaft. A lubricating film is thus formed in a clearance between the external circumferential surface of the shaft and the inner circumferential surface of the bearing. Accordingly, the shaft is supported by hydrodynamic shearing stress and dynamic pressure generated by the lubricating film when the lubricant flows through different cross-sections. However, the dynamic pressure is not smooth due to perpendicular, step-like boundaries 110 of the herringbone-shaped grooves as shown in FIG. 9. The perpendicular, step-like boundaries cause a sudden dynamic pressure change while the lubricant flows through the boundaries. Consequently, the sudden dynamic pressure results in unsteady rotation of the shaft.
A related method for manufacturing a hydrodynamic bearing 50 shown in FIG. 10 comprises following processes of: (a1) manufacturing a bearing 52 with a bearing hole 54 therein; and (a2) defining a plurality of hydrodynamic pressure generating grooves 56 in a bearing surface 55 of the bearing 52 by chemical etching, electrolysis electric discharge or machining. However, the small size of the hydrodynamic bearing 50 results in difficulties in particularly in the making of the grooves 56 in the bearing surface 55 of the bearing 52. This makes manufacturing of the hydrodynamic bearing 50 both time-consuming and expensive. Therefore, the related method is not suitable for mass-production of the hydrodynamic bearing 50.
It is therefore desirable to provide an improved method for mass production of a hydrodynamic bearing which can provide a steady hydrodynamic pressure.